Considerable attention has been directed toward repairing rather than replacing structural components, such as railroad ties, as a more efficient economic means for extended use of the whole structure. When a section of rail needs replacing or during routine maintenance of the railroad, the rail is detached from the ties by removing the spikes and tie plates, leaving behind railroad ties having spike holes.
Before these railroad ties can be re-used, the spike holes must be plugged to provide the tie with structural integrity and prevent water from accumulating within the hole and rotting the wood. Various methods to plug spike holes have been proposed, including driving wooden dowels or metal inserts through the hole. These methods, however, are labor intensive and often leave gaps between the insert and tie through which water can accumulate and deteriorate the wood.
An alternative approach suggested in the art is to plug the spike holes with a high density rigid polyurethane foam. As pointed out in U.S. Pat. No. 4,661,532 to Morin, however, the presence of environmental water or moisture in the hole causes the injected polyurethane composition to foam uncontrollably resulting in an undesirable low density foamed mass having low strength. As a solution to this problem, Morin proposed using a urethane composition made hydrophobic by adding a coal tar or a coal tar pitch to the urethane composition, thereby repelling any environmental water present and preventing the water from reacting with the foam ingredients. However, coal tar pitch is predominately composed of polynuclear aromatic compounds among which are volatile components carcinogenic to humans such as anthracene, phenanthrene, and acridine. Likewise, coal tar is a known carcinogen and contains numerous aromatic volatiles toxic by inhalation.
Consequently, the inventors herein have set out to search for a suitable alternative to coal tar based rigid polyurethane foam compositions which will prevent the urethane composition from reacting with environmental water or moisture on or in the application site while reducing the carcinogenic health risks associated with the aromatic compounds contained within coal tar.